Fix Android Top Activity (MvvmCross#4290)

* Fix Android Top Activity, old code was overcomplicated

* Fix layouts using old types

MvvmCross.Forms/Platforms/Android/Views/MvxFormsAppCompatActivity.cs

@@ -98,7 +98,7 @@ protected override void OnCreate(Bundle bundle)
         {
             // ensuring mvvmcross is running here is required
             // otherwise app will crash when inflating the view because of the Forms base class
-            var setup = MvxAndroidSetupSingleton.EnsureSingletonAvailable(ApplicationContext);
+            var setup = MvxAndroidSetupSingleton.EnsureSingletonAvailable(this);
             setup.EnsureInitialized();
 
             base.OnCreate(bundle);

MvvmCross.Forms/Platforms/Android/Views/MvxFormsApplicationActivity.cs

@@ -96,7 +96,7 @@ protected override void OnCreate(Bundle bundle)
         {
             // ensuring mvvmcross is running here is required
             // otherwise app will crash when inflating the view because of the Forms base class
-            var setup = MvxAndroidSetupSingleton.EnsureSingletonAvailable(ApplicationContext);
+            var setup = MvxAndroidSetupSingleton.EnsureSingletonAvailable(this);
             setup.EnsureInitialized();
 
             base.OnCreate(bundle);

MvvmCross/Platforms/Android/Core/IMvxAndroidSetup.cs

@@ -1,14 +1,16 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MS-PL license.
 // See the LICENSE file in the project root for more information.
 
-using Android.Content;
+using Android.App;
 using MvvmCross.Core;
 
 namespace MvvmCross.Platforms.Android.Core
 {
+#nullable enable
     public interface IMvxAndroidSetup : IMvxSetup
     {
-        void PlatformInitialize(Context applicationContext);
+        void PlatformInitialize(Activity activity);
     }
+#nullable restore
 }

MvvmCross/Platforms/Android/Core/MvxAndroidSetup.cs

@@ -24,27 +24,40 @@
 using MvvmCross.Views;
 using MvvmCross.Presenters;
 using System.Linq;
+using Android.App;
 
 namespace MvvmCross.Platforms.Android.Core
 {
 #nullable enable
     public abstract class MvxAndroidSetup
         : MvxSetup, IMvxAndroidGlobals, IMvxAndroidSetup
     {
-        private Context? _applicationContext;
+        private MvxCurrentTopActivity? _currentTopActivity;
         private IMvxAndroidViewPresenter? _presenter;
 
-        public void PlatformInitialize(Context applicationContext)
+        public void PlatformInitialize(Activity activity)
         {
-            if (applicationContext == null)
-                throw new ArgumentNullException(nameof(applicationContext));
+            if (activity == null)
+                throw new ArgumentNullException(nameof(activity));
 
-            _applicationContext = applicationContext;
+            PlatformInitialize(activity.Application);
+        }
+
+        public void PlatformInitialize(Application application)
+        {
+            if (application == null)
+                throw new ArgumentNullException(nameof(application));
+
+            if (_currentTopActivity != null)
+                return;
+
+            _currentTopActivity = new MvxCurrentTopActivity();
+            application?.RegisterActivityLifecycleCallbacks(_currentTopActivity);
         }
 
         public virtual Assembly ExecutableAssembly => ViewAssemblies?.FirstOrDefault() ?? GetType().Assembly;
 
-        public Context? ApplicationContext => _applicationContext;
+        public Context? ApplicationContext => _currentTopActivity?.Activity?.ApplicationContext;
 
         protected override void InitializeFirstChance(IMvxIoCProvider iocProvider)
         {
@@ -78,17 +91,10 @@ protected virtual void InitializeAndroidCurrentTopActivity(IMvxIoCProvider iocPr
 
         protected virtual IMvxAndroidCurrentTopActivity CreateAndroidCurrentTopActivity()
         {
-            var mvxApplication = MvxAndroidApplication.Instance;
-            if (mvxApplication != null)
-            {
-                var activityLifecycleCallbacksManager = new MvxApplicationCallbacksCurrentTopActivity();
-                mvxApplication.RegisterActivityLifecycleCallbacks(activityLifecycleCallbacksManager);
-                return activityLifecycleCallbacksManager;
-            }
-            else
-            {
-                return new MvxLifecycleMonitorCurrentTopActivity(Mvx.IoCProvider.GetSingleton<IMvxAndroidActivityLifetimeListener>());
-            }
+            if (_currentTopActivity == null)
+                throw new InvalidOperationException($"Please call {nameof(PlatformInitialize)} first");
+
+            return _currentTopActivity;
         }
 
         protected virtual void InitializeLifetimeMonitor(IMvxIoCProvider iocProvider)
@@ -123,10 +129,10 @@ protected sealed override IMvxViewsContainer CreateViewsContainer(IMvxIoCProvide
         {
             ValidateArguments(iocProvider);
 
-            if (_applicationContext == null)
+            if (ApplicationContext == null)
                 throw new InvalidOperationException("Cannot create Views Container without ApplicationContext");
 
-            var container = CreateViewsContainer(_applicationContext);
+            var container = CreateViewsContainer(ApplicationContext);
             iocProvider.RegisterSingleton<IMvxAndroidViewModelRequestTranslator>(container);
             iocProvider.RegisterSingleton<IMvxAndroidViewModelLoader>(container);
             var viewsContainer = container as MvxViewsContainer;

MvvmCross/Platforms/Android/Core/MvxAndroidSetupSingleton.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MS-PL license.
 // See the LICENSE file in the project root for more information.
 
+using Android.App;
 using Android.Content;
 using MvvmCross.Core;
 
@@ -10,10 +11,17 @@ namespace MvvmCross.Platforms.Android.Core
     public class MvxAndroidSetupSingleton
         : MvxSetupSingleton
     {
+        public static MvxAndroidSetupSingleton EnsureSingletonAvailable(Activity application)
+        {
+            var instance = EnsureSingletonAvailable<MvxAndroidSetupSingleton>();
+            instance.PlatformSetup<MvxAndroidSetup>()?.PlatformInitialize(application);
+            return instance;
+        }
+
         public static MvxAndroidSetupSingleton EnsureSingletonAvailable(Context applicationContext)
         {
             var instance = EnsureSingletonAvailable<MvxAndroidSetupSingleton>();
-            instance.PlatformSetup<MvxAndroidSetup>()?.PlatformInitialize(applicationContext);
+            instance.PlatformSetup<MvxAndroidSetup>()?.PlatformInitialize(applicationContext as Application);
             return instance;
         }
     }

MvvmCross/Platforms/Android/Services/MvxBroadcastReceiver.cs

@@ -5,7 +5,6 @@
 using System;
 using Android.Content;
 using Android.Runtime;
-using MvvmCross.Core;
 using MvvmCross.Platforms.Android.Core;
 
 namespace MvvmCross.Platforms.Android.Services
@@ -24,7 +23,7 @@ protected MvxBroadcastReceiver()
 
         public override void OnReceive(Context context, Intent intent)
         {
-            var setup = MvxAndroidSetupSingleton.EnsureSingletonAvailable(context);
+            var setup = MvxAndroidSetupSingleton.EnsureSingletonAvailable(context.ApplicationContext);
             setup.EnsureInitialized();
         }
     }

MvvmCross/Platforms/Android/Views/MvxActivityViewExtensions.cs

@@ -152,7 +152,7 @@ private static void EnsureSetupInitialized(this IMvxAndroidView androidView)
             }
 
             var activity = androidView.ToActivity();
-            var setup = MvxAndroidSetupSingleton.EnsureSingletonAvailable(activity.ApplicationContext);
+            var setup = MvxAndroidSetupSingleton.EnsureSingletonAvailable(activity);
             setup.EnsureInitialized();
         }
     }

MvvmCross/Platforms/Android/Views/MvxCurrentTopActivity.cs

@@ -0,0 +1,60 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MS-PL license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using Android.App;
+using Android.OS;
+using Android.Runtime;
+
+namespace MvvmCross.Platforms.Android.Views
+{
+#nullable enable
+    [Register("mvvmcross.platforms.android.MvxCurrentTopActivity")]
+    public class MvxCurrentTopActivity
+        : Java.Lang.Object, Application.IActivityLifecycleCallbacks, IMvxAndroidCurrentTopActivity
+    {
+        [Weak]
+        private Activity? _lastSeenActivity;
+
+        public Activity? Activity => _lastSeenActivity;
+
+        public static bool Initialized { get; set; }
+
+        public void OnActivityCreated(Activity activity, Bundle? savedInstanceState)
+        {
+            _lastSeenActivity = activity;
+        }
+
+        public void OnActivityPaused(Activity activity)
+        {
+            _lastSeenActivity = activity;
+        }
+
+        public void OnActivityResumed(Activity activity)
+        {
+            _lastSeenActivity = activity;
+        }
+
+        public void OnActivityDestroyed(Activity activity)
+        {
+            // not interested in this
+        }
+
+        public void OnActivitySaveInstanceState(Activity activity, Bundle outState)
+        {
+            // not interested in this
+        }
+
+        public void OnActivityStarted(Activity activity)
+        {
+            // not interested in this
+        }
+
+        public void OnActivityStopped(Activity activity)
+        {
+            // not interested in this
+        }
+    }
+#nullable restore
+}